Radiation oncology is the medical specialty concerned with prescribing and delivering radiation, and is distinct from radiology—the use of radiation in medical imaging and diagnosis. Radiation may be prescribed by a radiation oncologist with intent to cure (“curative”) or for adjuvant therapy. It may also be used as palliative treatment (where cure is not possible and the aim is for local disease control or symptomatic relief) or as therapeutic treatment (where the therapy has survival benefit and it can be curative). It is also common to combine radiation therapy with surgery, chemotherapy, hormone therapy, immunotherapy, or some combination of the four.
Most common cancer types can be treated with radiation therapy in some way. The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on the tumor type, location, and stage, as well as the general health of the patient. Total body irradiation (TBI) is a radiation therapy technique used to prepare the body to receive a bone marrow transplant. Brachytherapy, in which a radiation source is placed inside or next to the area requiring treatment, is another form of radiation therapy that minimizes exposure to healthy tissue during procedures to treat cancers of the breast, prostate and other organs.
Radiation therapy also has several applications in non-malignant conditions, such as the treatment of trigeminal neuralgia, acoustic neuromas, severe thyroid eye disease, pterygium, pigmented villonodular synovitis, and prevention of keloid scar growth, vascular restenosis, and heterotopic ossification. The use of radiation therapy in non-malignant conditions is limited partly by worries about the risk of radiation-induced cancers.
Radiation therapy works by damaging the DNA of e.g., cancerous cells, and thus itself has the potential for causing cancers. The DNA damage is caused by one of two types of energy, photon or charged particle. This damage is either direct or indirect ionization of the atoms that make up the DNA chain. Indirect ionization happens as a result of the ionization of water, forming free radicals, notably hydroxyl radicals, which then damage the DNA.
There are many different types of radiation therapies. External beam radiation therapy (XRT) is delivered via two- or three-dimensional beams using linear accelerator machines and is commonly used to treat prostate, breast and other tumors. In XRT treatment of the prostate, as an example, radiation is directed along different axes to the target prostate, which is near the rectal wall and surrounds the urethra. Where the beams cross, the radiation dose is the highest, and thus the prostate can be preferentially targeted. Misdirected radiation beams may perforate the rectal wall causing radiation proctitus (rectal bleeding), as well as erectile dysfunction (ED), incontinence and other complications. In fact, as many as half of the treated men suffer from ED and/or incontinence. Thus, it can be seen that that narrowly targeting the radiation is critical for reducing side effects.
For breast cancers, the risks are less severe than with XRT treatment of the prostate, because large volumes of lung and heart are typically not included in the target field. However, the risk is not eliminated and organs at risk include the breast and underlying muscle, ribs, lung, and heart. Cardiac complications are due to myocardial cell damage, the consequences of which can be seen decades after XRT. Lung toxicity (fibrosis) occurs with lower doses and is volume related. Secondary lung cancers may be observed many decades after XRT. There is also an increased risk of non-breast malignancies (relative risk [RR]=4.32) and of cardiovascular deaths (RR=2.04) from postmastectomy XRT in patients followed for 25 years. Other less serious risks, although significant to the affected individual, include lymphedema, breast fibrosis and pain, skin changes, rib fractures, and unsuccessful reconstruction.
There are several variations on XRT, including conventional radiation therapy (2DXRT), 3-dimensional conformal radiation therapy (3DCRT), stereotactic radiation, stereotactic radiosurgery, intensity-modulated radiation therapy (IMRT), image-guided radiation therapy (IGRT) or four-dimensional radiation therapy, which provide ever improving methods of targeting the tumor sites and planning the overall treatment.
In particle therapy (proton therapy being one example), energetic ionizing particles (protons or carbon ions) are directed at the target tumor. The dose increases while the particle penetrates the tissue, up to a maximum (the Bragg peak) that occurs near the end of the particle's range, and it then drops to (almost) zero. The advantage of this energy deposition profile is that less energy is deposited into the healthy tissue surrounding the target tissue.
Brachytherapy (internal radiation therapy) is delivered by placing radiation source(s) inside or next to the area requiring treatment. Brachytherapy is commonly used as an effective treatment for cervical, prostate, breast, and skin cancer and can also be used to treat tumours in many other body sites.
Intraoperative radiation therapy (IORT) is applying therapeutic levels of radiation to a target area, such as a cancer tumor, while the area is exposed during surgery. The goal of IORT is to improve local tumor control and survival rates for patients with different types of cancer.
Dosage is always an important concern in treating any tumor or disease using radiation therapy. The dose should be enough to kill malignant cells, but tightly targeted so as to minimize damage to the surrounding healthy tissue. However, since patient tissues and organs are rarely immobile, the oncologist must allow a slightly increased area target to allow for movements caused by e.g., breathing, peristalsis, muscle contractions, and the like, and still ensure the tumor or other diseased area is adequately treated. This additional treatment zone surrounding the target is known as a “margin.”
Skin lesions and other superficial cancers can occur on irregularly shaped body parts, such as the head, face and neck. The irregular shapes make it difficult to plan and administer an optimum radiation dose to the treatment site. These surfaces require smoothing to achieve uniform doses at depth and proper buildup of dose at the surface. The surface smoothing and dose buildup is achieved by applying a “bolus.” To deliver a known dose, produce a known central axis depth dose, and beam flatness for successful treatment, it is necessary that water or tissue equivalent bolus material is used.
FIG. 1 shows the effect of bolus on e.g., electron beam depth dose. The depth dose curve starts from the surface of the bolus, so from the point of view of the underlying patient tissue, the depth dose is shifted up. The skin dose is thus increased, and the dose at depth (below the target volume) is reduced. The addition of a bolus shifts the treatment depth upwards, so that conformal bolus use can also be helpful in shaping a variable depth of treatment, as shown in FIG. 2.
Several moldable materials, currently or formerly used in dental clinics, have been evaluated as tissue equivalent bolus materials. Polyflex, a hydrocolloid from DentsPly® was found to be near water equivalent for electron and photon beams. It was also inexpensive, readily available, and held up well over time. Another commercially available bolus material is Aquaplast RT® thermoplastic from WFR®. Aquaplast RT™ is a new type of bolus material that can be easily molded and conformed to the curvature of skin, with the equivalence to soft tissue in radiation interaction. Another commercially available material is Jeltrate® Plus from DentsPly®. Other materials investigated for bolus use include solid water, paraffin, superflab, wet gauze, wet sheets, PlayDoh®, and gauze embedded with petroleum jelly.
Because of concern over dosimetry and dosage uniformity, many companies are developing dosimeters that allow real time radiation dosage measurements, so that dosage can be more precisely controlled, rather than estimated.
Plastic scintillation detectors (PSDs) are promising as dosimeters for in vivo dosimetry due to their favorable dosimetric characteristics, including water-equivalence, energy independence, dose linearity, and resistance to radiation damage. Once calibrated, PSDs do not require conversion and/or correction factors as needed for some other commonly used detectors to convert the dosimeter reading to absorbed dose. Furthermore, due to their small detecting volume, plastic scintillation detectors exhibit excellent spatial resolution. The plastic scintillating element in a PSD consists of organic scintillating molecules in a polymerized solvent that emits light proportionally to the ionizing radiation dose delivered to its sensitive volume. The light is emitted within nanoseconds and therefore PSDs can be used for real-time applications. The scintillation light produced is transmitted to a photodetector using a clear optical fiber guide.
The use of plastic optical fiber as optical guides makes the PSDs completely water-equivalent and will not perturb the energy deposition process. One drawback concerning these detectors is the radiation-induced light arising in the optical fibers, a combination of Cerenkov emission and fluorescence. This phenomenon has been addressed by several investigators, and a difference in the ratio between measured and expected dose values of PSD measurements being less than 1% has been achieved. These detectors have not yet been accepted into standard clinical practice, because until recently they were not commercially available.
Several skin patch sensors are available, but most are simple sensors attached to an adhesive patch, and many are not capable of real time dosimetry. Further, none have been combined with bolus, so as to allow uniform distribution over irregular surfaces.
US20100127181, titled Radiation Sensor Arrays For Use With Brachytherapy, provides disposable single-use radiation sensor patches using MOFSETs that have adhesive means onto the skin of a patient to evaluate the radiation dose delivered during a treatment session. The sensor patches are configured to be minimally obtrusive and operate without the use of externally extending power chords or lead wires. However, the skin patch is conventional. Additionally, the system is not real time, requiring the oncologist contact the sensor patch with a dose-reader device after the administering step to obtain data associated with a change in an operational parameter in the dosimeter sensor patch. U.S. Pat. No. 7,897,927 describes readers for same.
What is needed in the art are even better skin sensors for dosimetry. Such sensors would preferably be capable of real time dosimetry and cost effective, as well as combinable with bolus.